STP Technical Class: Explaining Scope
Posted on January 16 2019
Emtron features a built-in Scope for all ECU types. Depending on the ECU (or if a plugin model – the type it is based on), the number of channels that can be scoped is variable:
|SL4||Crank, Sync Sensor|
|SL6||Crank, Sync Sensor|
|SL8||Crank, Sync Sensor|
|KV8||Crank, Sync Sensor, DI 1-4|
|KV12||Crank, Sync Sensor, DI 1-8|
|KV16||Crank, Sync Sensor, DI 1-8|
|KV16M||Crank, Sync Sensor, DI 1-8|
Access Scope under
- Utilities, Scope
When you select Scope, it opens a new window with the Scope.
The scope function records the channel assignments to internal memory when started/stopped with the buttons at the top right. The memory can be subsequently downloaded, erased, saved, and loaded by the other buttons in the utility.
Configuration details are as follows:
- Purple: Select what channel to display and whether you want the trace to be visible or not.
- Red: Change the volts per division for each channel. The chart is divided into blocks up and down. Each block equals 2 volts in the above example.
- Orange: The traces can be offset so they do not overlay on top of each other. The default value is 0.00V, meaning the voltage will trace from the center (so it will read +/- 0V). It is useful to offset the traces, so they can be all visible at the same time on the chart as in the above example.
- Green: Sec Offset moves the trace to a specific position
- Blue: Time Sec Per Div changes the zoom level of the scope by adjusting the time per division horizontally. Like voltage per division vertically. After starting and stopping the scope, this will need to be adjusted until a trace draws an appropriate picture as in the example above.
- Light Blue: Sample Rate should be adjusted to set the scope recording rate. In most cases, the default value of 10ksps should be enough, but if scope traces are requested for troubleshooting purposes (on running engines for example – not just for trigger decoding requests), then a higher speed may be requested.
** Note a higher sampling rate will use up the Emtron internal memory much faster. A shorter period of recording should be anticipated (a few seconds generally).
Uses of Scope
While Emtron supports a high number of trigger types, there is occasionally the need to add new engine types. The fastest way to get support for a new engine type is to provide Emtron directly with scope file directly from the Emtune software (exported from the Scope Utility as a .esf file). If the vehicle has VVT (variable valve timing), please contact support for any special instructions. A cranking scope trace with cylinder 1 spark plug removed (or only cylinder 1 spark plug installed) can be helpful in identifying an approximation of crank index offset position.
* The cranking speed will speed up/slow down at the point of compression
Troubleshooting Trigger Errors
There are several runtimes the ECU generates to diagnose/validate triggers the ECU is using. You can see these runtimes live under:
- Runtimes, Triggers/Limits, Engine Decoding/Engine Decoding Status
** Green runtimes simply are notifications that there is a “signal” present on these inputs. They do not signify if the signals are valid.
Improper Crank/Sync Sensor Arming Threshold Settings
When the Arming Threshold for Crank or Sync sensors is not set correctly, Crank or Crank/Sync errors are generally the results causing error count, misfires, no start conditions, etc. The Scope can help identify the issues and allow configuration changes to fix the errors.
The above example shows a crank trigger with a Crank Sensor Arming Threshold set too low (represented by the green line) – 0.5v). Setting the Arming Threshold (as described in Crank/Sync Sensor Arming Threshold), states for the signal to be valid the voltage must go above this voltage.
The above example shows the signal crossing the arming voltage (red arrows) twice, and subsequently in purple where the ECU is triggering a “tooth” position as a result of the signal. One clearly is a tooth, and one is a false trigger. Lifting the arming voltage above the false trigger in this situation will filter out the second erroneous trigger.
** A normal characteristic of a magnetic sensor requires lifting of the voltage as the RPM of increases. This is a good characteristic of a magnetic trigger anyways, as since the voltage of the sensor is increasing, you can filter out any interference in the lower voltage ranges as well. Emtron trigger inputs can also handle high signal amplitude (100V +/-).
A good example of Sync Sensor Arming Threshold = 2.5v.
The polarity of Crank/Sync sensor
During most start-up support, we often encounter reversed polarity of crank/sync sensors. The Scope can be used to easily identify the issues. These polarity situations are especially sensitive when using missing tooth triggers due to the gap position affecting the index tooth position (see Crank Index Position), or not being able to be recognized at all. When the trigger tooth passes the sensor, the magnetic sensor should produce a positive voltage before dropping voltage negative.
This is easier to identify on a trigger wheel with a lower tooth count as you can see above.
On a trigger wheel with multi-tooth, it is more difficult to identify polarity.
For multi-tooth wheels with a missing tooth – Use the gap to identify the polarity of this crank sensor is correct. Do this by ensuring that the next tooth after the gap rises before it falls.
On a non-missing tooth multi-tooth trigger, the polarity can be validated generally by observing the “fast edge” being the falling edge. The above example shows this where the rising slope of the trace is much slower than the falling slope of the trace. The rising slope also will change based on the speed of the trigger wheel.
** Note – this is also why the falling edge provides most stable timing on magnetic triggers (with correct polarity).
** See Crank Index/Sync Sensor Setup
Crank trigger wired with incorrect polarity. Observe the voltage drops as the tooth after the gap approaches instead of rises.
In the case of missing tooth trigger wired with backward polarity, the index tooth would either be recognized in the wrong position (earlier/before the index tooth has passed), or the “gap” not recognized properly due to not being able to differentiate a clear space. Subsequently, this does not allow the ECU to identify the index tooth for timing the engine. Additionally, the uneven spacing (besides the expected “gap tooth number”) will cause the ECU to count crank tooth errors. The gap between the “false” index tooth position/gap and evenly spaced teeth will change with RPM as well.
Crank trigger wired with correct polarity. Observe the voltage rises as the tooth after the gap approaches. With the polarity correct, it is clear the gap can be recognized, and the index tooth is being appropriately recognized as the true position (tooth after the gap).
Improper Edge Configuration for Crank/Sync Sensor
With correct sensor polarity, both magnetic and hall sensors should have falling edge polarity in most cases. This is because these sensors have consistent “fast” performance when the tone ring teeth pass the sensors.
An example of a magnetic sensors fast edge being the falling.
An example of a hall sensor fast edge being the falling. Most hall sensors produce a very good “square” wave, so the point can be argued that rising edge can be used, however at higher revs some will produce this “sawtooth” pattern which means triggering that way will cause timing to wander.
Rising and Falling Edge Sync Mode
Engines with multi-tooth sync sensors usually will have a “long” tooth during the “crank index point”. Normally, a custom decoding mode is needed to run the engine with multiple sync teeth, but in this case because there is a clear difference in signal on the sync input on each stroke (low vs high), the ECU can determine the stroke immediately (this is the fastest way to decode starting/720 sync). Set Sync Sensor Edge configuration to Rising and Falling for these trigger types.
** See Sync Sensor Setup – Edge Rising/Falling mode
Scope Voltage Clipping
The scope can only read +/- 25v. Anything over 25v (regardless of input specifications) will display signals that can be misconstrued as an error.
Above is an example of the scope “clipping” over its 25v limit. This is normal and should not be considered an error in the signal.
** If signals need to be measured reliably +/- 25v, then an external scope tool must be used.
We at STP hope that this Technical Blog can help solve any issues you may be facing. Stay tuned for more Technical Blogs.
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